An optimized relaying method for multi-antennas cooperative networks, estimate-and-forward (EF) strategy for MIMO relay, is proposed and analyzed in this paper. According to our theoretical analysis, it performs like amplify-and-forward (AF) for the low signal noise ratio (SNR) region and behaves like detect-and-forward (DF) for the high SNR region. For the relay networks with a large number of antennas and/or high order constellations, two approximate methods are proposed to reduce the complexity of the signal estimation at the relay. The first one uses a list sphere decoder to generate an estimate list and to obtain the approximate minimum mean squared error (MMSE) estimate based on the reduced list. The proposed list EF retains the advantages of the exact EF relay strategy in large MIMO relay networks at a negligible performance loss. The second algorithm computes the estimate of the symbols using Gaussian approximation to approximate the summation to be integral. We find the proposed EF scheme performs better than both AF and DF across all SNRs without switching algorithms for different SNRs.